Alfven wave heating

The authors have shown that an efficient heating mechanism exists at frequencies below the ion cyclotron frequency range which involves conversion of the Alfven wave into a slow mode which is strongly absorbed by electron Landau damping. Experiments have demonstrated the possibility of efficiently delivering energy to a plasma under alfven resonance conditions and heating both the electrons and ions. Thus far, the experiments have been on a small scale. The largest experiments have been done on the TCA tokamak with rf input powers of up to 200 kW (close to the ohmic heating power) and have raised the peak electron and ion temperatures by 200 and 140 eV, respectively, at a density on the order of 3 · 1013 cm-3. This corresponds to ηh ∼ 5 · 1013 eV/(cm3 · kW). It should be noted that a whole series of physical questions associated with Alfven heating are still unanswered. The major technical problem in realizing Alfven heating is to develop an antenna system which, according to the conditions for exciting the alfven resonance, must have a length comparable to the circumference of the torus and cover a large fraction of the vacuum vessel surface (although the rf current leads can be relatively small). This would lead to considerable difficulties in constructing vacuum vessels for large machines or a reactor